CAREER: Nucleophilic Cobalt Photocatalysis for the Generation of Radicals from Non-Traditional Precursors

With the support of the Chemical Catalysis Program in the Division of Chemistry and the Established Program to Stimulate Competitive Research (EPSCoR), Spencer Pitre of Oklahoma State University is developing cobalt catalysts to generate carbon radicals from non-traditional precursors using visible light irradiation. Carbon radicals have become an indispensable tool for the construction of complex organic molecules.

However, most organic compounds must be preactivated to be effective as radical precursors, adding undesired synthetic steps and creating additional byproducts and chemical waste. Inspired by Vitamin B12 and its natural reactivity, Dr. Pitre and his research group are leveraging analogous cobalt complexes to generate carbon radicals from new classes of precursors, avoiding the need for preactivated substrates.

These methods rely on visible light photochemistry to mediate radical formation, an emerging synthetic strategy that enables mild reaction conditions. Despite its importance to the field of organic chemistry, students at the undergraduate level do not receive any exposure to photochemistry in the traditional curriculum. This omission is being addressed through an annual undergraduate photochemistry workshop, which gives students that have limited access to research opportunities from across Oklahoma the chance to learn about photochemistry and its impact on the development of new chemistries.

These research effort will also serve to train a diverse group of graduate and undergraduate researchers in photochemistry and catalysis.

Cobaloximes, which mimic the reactivity of the cobalt atom of Vitamin B12, are among the strongest nucleophiles known when in the Co(I) oxidation state and can undergo SN2 reactions with electrophiles. The resulting alkyl–cobalt can undergo facile homolytic cleavage when irradiated with visible light to generate carbon-centered radicals. Despite having similar nucleophilicities, cobaloximes are generally less efficient than Vitamin B12 at catalyzing radical generation from electrophilic substrates.

Dr. Pitre and his research team are probing the effect of the axial ligands on each step of the catalytic cycle to develop more efficient nucleophilic cobalt photocatalysts. These nucleophilic cobalt photocatalysts are being tuned to enable radical formation from new classes of precursors, including chloroform, electron-deficient alkenes, iminium ions and vinyl halides and triflates.

If successful, these studies will expand understanding of cobaloxime chemistry and enhance the potential for the development and deployment of Co(I) cobaloxime catalytic systems.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.